1. Field of the Invention
This invention pertains to a process for recovering volatile organic materials consisting essentially of carbonyl compounds from spent solvent-in-water emulsions derived from paint overspray treatment and capture systems. More specifically, this invention pertains to a process whereby carbonyl compounds are recovered from spent solvent-in-water emulsions derived from paint overspray treatment and capture systems in a manner which permits their successful reuse.
2. Discussion of the Relevant Art
Operation of paint spray booths using solvent-in-water emulsions which permit the collection of hydrocarbon emissions from paint solvents, solubilizing various types of paints, and dispersion and collection of both solubilized and non-solubilized solids has been set forth in numerous references. Discussion of formulations employing carbonyl compounds in solvent-in-water emulsions for use in paint spray booths is discussed in U.S. Pat. Nos. 5,198,143; 5,397,496, 5,200,104 and 5,254,256 all to Zuerner et al, the specifications of which are incorporated by reference in this document.
Solvent-in-water emulsions employed in the paint spray booths serve as a replacement for a conventional water system and act as a collection medium for hydrocarbon vapors and for paint overspray. The paint overspray contacts the solvent-in-water circulating in the paint spray booth. The material is solubilized and the paint solids are dispersed within the solvent-in-water emulsion. The paint solids are recirculated within the solvent-in-water emulsion until the solvent-in-water emulsion is separated from the paint spray booth system. Spent solvent-in-water emulsions containing paint solids are chemically broken or allowed to break into separate phases as parts of the recovery process. These separated phases are generally an organic phase containing solubilized paint solids and an aqueous phase. The separated phases are then treated and reused or disposed of as appropriate. For instance, Patzelt U.S. Pat. No. 4,919,691 suggests the use of recovered aqueous portions of spent emulsion in recycled solvent-in-water emulsion materials. However, no effective method of direct, efficient recovery of the organic solvent portion of spent solvent-in-water emulsions has been discovered to date.
It is well-accepted that recovery of the organic solvent component from spent solvent-in-water emulsions derived from the overspray treatment and capture system is necessary and desirable to maximize efficiency and economy in the overall paint overspray treatment process. The recovered organic solvent component should be suitable for reuse in the paint overspray treatment and capture system. However a significant portion of the organic solvent component has remained unrecoverable due to the presence of and interaction with paint solids during the recovery process. The paint solids in the spent emulsion make it difficult to effectively recover any significant amount of relatively pure organic solvent. Separation of the organic solvent component from the paint solids was so difficult because a large portion of the solvent remained bonded with the paint solids and was essentially non-recoverable.
Various techniques have been suggested for separating solvent from spent solvent-in-water emulsions derived from paint overspray treatment and capture systems. In these techniques, the presence of paint solids derived from the paint overspray treatment system creates problems of solvent retention and thermal decomposition of the paint solids during recovery processes. Temperatures necessary to accomplish volatilization of the organic solvent have resulted in uneven solidification of the paint solids thereby trapping a significant amount of the organic solvent in the solidifying paint solids mass. Additionally, the processing temperatures necessary to volatilize the organic solvent has also resulted in thermal decomposition of the paint solids. The thermally decomposed solids are difficult not only to remove from any reaction vessel but also to handle once removed.
Thus, it is desirable to provide a process whereby organic carbonyl compound materials can be efficiently and successfully recovered from spent solvent-in-water emulsion systems derived from paint overspray treatment and capture systems. It is also desirable to provide a process in which carbonyl compound materials such as secondary alcohol esters and secondary alcohol ester derivatives can be recovered in a continuous manner without causing the thermal decomposition of remaining solid compounds.